Lubricant composition and bearing

ABSTRACT

There are provided a lubricant composition for use in a ball-and-roller bearing with a smaller diameter, and a ball-and-roller bearing with a smaller diameter. The lubricant composition comprises a base oil comprising a non-ester oil containing a synthesized hydrocarbon oil, and a thickener comprising a urea compound; wherein the urea compound is represented by the formula (I):  
     R 1 —(NHCONH—R 2 )n  (I) 
     where R 1  is a group containing an aromatic hydrocarbon, R 2  is at least one hydrocarbon group selected from the group consisting of an alicyclic hydrocarbon group having 6 to 12 carbon atoms and an aliphatic hydrocarbon group having 6 to 20 carbon atoms, and n is 2 or 3; wherein the synthesized hydrocarbon oil has kinetic viscosity of 20 mm 2 /s or more and less than 80 mm 2 /s at 40° C.; and wherein the base oil comprises 50% by weight or more of the synthesized hydrocarbon oil based on the total weight of the base oil.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a lubricant composition, and a bearing prelubricating the lubricant composition. More particularly, the present invention relates to a lubricant composition for a ball-and-roller bearing with a smaller diameter, and the ball-and-roller bearing with a smaller diameter applicable to an electronic information recording and reading apparatus such as a hard disk drive (HDD) that is needed to rotate with low noise for a long period of time.

[0003] 2. Discussion of Background

[0004] Ball-and-roller bearings are used in various types of electronic information recording and reading apparatuses, i.e., a magnetic recording and reading apparatus such as a hard disk drive (HDD) and a video tape recorder (VTR), a printing apparatus such as a laser beam printer (LBP), and an optical apparatus such as a compact disk (CD), a CD-ROM, a digital video disk (DVD), and a DVD-ROM. The ball-and-roller bearing is required to have low torque and excellent acoustic properties in order to decrease electric power consumption of such apparatuses, and to operate with low noise.

[0005] Such ball-and-roller bearing has a small diameter and is called as a miniature bearing. Conventionally, lubricating oil or grease is used for lubricating the ball-and-roller bearing with a small diameter.

[0006] Even though the lubricating oil or grease is applied to the conventional ball-and-roller bearing, a noise is apt to be produced. It is contemplated that the noise is produced because an oily film is poorly formed on a rolling surface of the bearing. In many cases, torque of the bearing is significantly changed when the noise is produced.

[0007] Japanese Patent Publication No. 8-209176 discloses a grease composition for improving acoustic properties of a bearing, and for prolonging the acoustic properties at high to low rotating speeds. The grease composition comprises not less than 5% by weight and less than 20% by weight of a thickener including 40 to 100% by weight of a lithium salt of a fatty acid having 12 to 24 carbon atoms and having no hydroxyl group, and a base oil with kinetic viscosity of 80 to 300 mm²/s at 40° C. including at least 10% by weight of an ester oil. Also disclosed is a grease composition comprising a thickener including 5 to 30% by weight of at least one of diurea and a polyurea, and a base oil including at least 10% by weight of an ester oil.

[0008] Japanese Patent Publication No. 11-325086 discloses a ball-and-roller bearing for a hard disk drive (HDD) prelubricating a grease, which comprises a base oil comprising an aromatic ester, or a mixture of an aromatic ester and a polyol ester, and a lithium soap type thickener. Such grease discharges less gases, and provides long-term acoustic properties.

[0009] The grease for the ball-and-roller bearing uses the lithium soap in the thickener and the ester oil in the base oil as described in Japanese Patent Publication No. 11-325086. While the grease provides excellent acoustic properties, there is easily induced wearing with minor moving, so-called “fretting corrosion” when the bearing in which the grease is prelubricated, or the apparatus in which the bearing is incorporated is moved or transported. The fretting corrosion might increase the noise upon rotating the bearing, which cannot keep silence, resulting in poor reliability of the bearing.

[0010] Also, the ester oil is used in the base oil, it is therefore difficult to prevent the fretting corrosion even if diurea or polyurea as the thickener is used.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide a lubricant composition prelubricating grease applicable to a bearing for use in an information recording and reading apparatus, which provides excellent acoustic properties and produces less fretting corrosion.

[0012] Another object of the present invention is to provide a bearing prelubricating the aforementioned lubricant composition.

[0013] The lubricant composition of the present invention comprises a base oil comprising a non-ester oil containing a synthesized hydrocarbon oil, and a thickener comprising a urea compound;

[0014] wherein the urea compound is represented by the formula (I):

R₁—(NHCONH—R₂)_(n)  (I)

[0015] where R₁ is a group containing an aromatic hydrocarbon, R₂ is at least one hydrocarbon group selected from the group consisting of an alicyclic hydrocarbon group having 6 to 12 carbon atoms and an aliphatic hydrocarbon group having 6 to 20 carbon atoms, and n is 2 or 3;

[0016] wherein the synthesized hydrocarbon oil has kinetic viscosity of 20 mm²/S or more and less than 80 mm²/s at 40° C.; and

[0017] wherein the base oil comprises 50% by weight or more of the synthesized hydrocarbon oil based on the total weight of the base oil. The term “non-ester oil” herein means an oil containing no ester oil.

[0018] The lubricant composition according to the present invention has worked penetration of 220 to 280, measured in accordance with Japanese Industrial Standard (JIS) K2220.

[0019] The bearing prelubricating the aforementioned lubricant composition is noise resistant and fretting corrosion resistant.

[0020] The bearing prelubricating the aforementioned lubricant composition is a spindle bearing for use in an apparatus for recording and reading information.

[0021] As described above, the bearing prelubricating the lubricant composition that comprises the base ester oil and the lithium soap type thickener can provide improved acoustic properties. However, the acoustic properties decrease when a synthesized hydrocarbon oil is used instead of the ester oil. On the other hand, the synthesized hydrocarbon oil can prevent the fretting corrosion. According to the present invention, the fretting corrosion can be prevented while keeping excellent acoustic properties by using the urea compound represented by the formula (I), even though the synthesized hydrocarbon oil is used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein:

[0023]FIG. 1 is a schematic cross-sectional view of a ball-and-roller bearing with a smaller diameter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] In the lubricant composition of the present invention, the base oil comprises the non-ester oil containing the synthesized hydrocarbon oil.

[0025] The synthesized hydrocarbon oil is a hydrocarbon compound including carbon and hydrogen. Examples include aliphatic hydrocarbon oils such as poly-α-olefine oil, a copolymer of α-olefine and olefine, and polybutene; aromatic hydrocarbon oils such as alkylbenzene, alkylnaphthene, polyphenyl, and synthesized naphthene.

[0026] Suitable synthesized hydrocarbon oil for use in the present invention is aliphatic hydrocarbon oils that can provides both acoustic properties and fretting corrosion resistance, when the urea compound is used as the thickener. Among them, poly-α-olefine, and a copolymer of α-olefine and olefine are preferable.

[0027] It is preferred that the synthesized hydrocarbon oil have kinetic viscosity of 20 mm²/s or more and less than 80 mm²/s at 40° C. If the kinetic viscosity of the synthesized hydrocarbon oil is less than 20 mm²/s, the resultant lubricant composition has poor heat resistance. On the other hand, if the kinetic viscosity exceeds 80 mm²/S, torque of the bearing increases. These tendencies depend on percentages of the synthesized hydrocarbon oil contained in the base oil.

[0028] Oil used as the base oil by mixing it with the synthesized hydrocarbon oil include a mineral oil such as naphthene, paraffin, liquid paraffin, and hydrodewaxed oil; a polyglycol oil such as polyalkylene glycol; an ether oil such as alkyldiphenyl ether, and polyphenyl ether; and a silicone oil such as polydimethyl siloxane, and polyphenyl methyl siloxane.

[0029] The base oil contains 50% by weight or more of the synthesized hydrocarbon oil based on the total weight of the base oil. The synthesized hydrocarbon oil alone may constitute the base oil. When the base oil contains 50% by weight or more of the synthesized hydrocarbon oil, the fretting corrosion can be prevented.

[0030] The urea compound used as the thickener is represented by the formula (I):

R₁—(NHCONH—R₂)_(n)  (I)

[0031] where R₁ is a group containing an aromatic hydrocarbon, R₂ is at least one hydrocarbon group selected from the group consisting of an alicyclic hydrocarbon group having 6 to 12 carbon atoms and an aliphatic hydrocarbon group having 6 to 20 carbon atoms, and n is 2 or 3. The urea compound can prevent the fretting corrosion, and improve acoustic properties.

[0032] In the formula (I), the R₁ has an aromatic single ring, an aromatic condensed ring, an aromatic single ring combined with methylene, cyanuric ring or isocyanuric ring, or an aromatic condensed ring combined with methylene, cyanuric ring or isocyanuric ring. Examples include a residual group in which an isocyanate group is eliminated from diphenylmethanediisocyanate, tolylenediisocyanate, or a diisocyanate polymer including dimer and trimer. When the R₁ is a group containing aromatic hydrocarbon, heat resistance of the lubricant composition can be improved.

[0033] The R₂ is an alicyclic hydrocarbon group having 6 to 12 carbon atoms, an aliphatic hydrocarbon group having 6 to 20 carbon atoms, or a hydrocarbon group containing them. When the R₂ has carbon atoms less than the defined range, heat resistance of the lubricant composition is decreased. On the other hand, when the R₂ has carbon atoms exceeding the defined range, the acoustic properties are decreased.

[0034] In the formula (I), R₁—(NHCONH—R₂)_(n), n is 2 to 3. In view of keeping thermal stability of the lubricant composition, it is preferred that n is 2 or 3.

[0035] The urea compound can be prepared by reacting an isocyanate compound with an amino compound. It is preferred that the isocyanate compound have approximately equivalent amino group as that of the amino compound in order to leave no reactive free radicals.

[0036] In the preparation of the lubricant composition, the isocyanate compound and the amino compound can be reacted in the base oil. Alternatively, the urea compound synthesized in advance can be mixed with the base oil. The former is the preferable preparing method, since the stability of the lubricant composition is easily kept.

[0037] The lubricant composition has worked penetration of 220 to 280. When the lubricant composition having worked penetration within this range is included within the ball-and-roller bearing with a smaller diameter, an oily film can be formed successfully on a rolling surface. Also, the fretting corrosion can be prevented.

[0038] Any known additives can be incorporated into the lubricant composition for improving the properties as required. Examples include an antioxidant including amines, phenolics, dithiozinc phosphates, or compounds containing sulfur; an extreme pressure agent including dithiozinc phosphate, organic molybdenum, or compounds containing chlorine, sulfur, or phosphorus; a rust preventive including petroleum sulfonates, dinonyl naphthalene sulfonates, or sorbitan esters; a metal deactivator including benzotriazole, or sodium nitrite; and a viscosity index improver including polymethacrylate, polyisobutylene, or polystyrene. These can be added alone or in combination.

[0039]FIG. 1 shows an example of the bearing according to the present invention. It is a schematic cross-sectional view of the ball-and-roller bearing with a smaller diameter.

[0040] The ball-and-roller bearing 1 comprises an inner ring 2 having a rolling surface on an outer surface, an outer ring 3 having a rolling surface on an inner surface and a plural rolling elements 4. The inner ring 2 and the outer ring 3 are concentrically disposed. Plural rolling elements 4 are disposed between the rolling surface of the inner ring 2 and the outer ring 3. The ball-and-roller bearing 1 also comprises a holder and a sealing member (both are not shown). The aforementioned lubricant composition 5 is filled between the inner ring 2 and the outer ring 3.

[0041] According to the present invention, the lubricant composition 5 prepared using the urea compound and the non-ester oil containing the synthesized hydrocarbon oil is applied to the bearing, thereby preventing the fretting corrosion that is likely to be produced on the rolling surface of the bearing. As the fretting corrosion is prevented, the noise of the rolling bearing will not be increased. As a result, the bearing moves silently. The bearing of the present invention can be used as a spindle bearing for use in an apparatus for recording and reading information, i.e., a magnetic recording and reading apparatus such as a hard disk drive (HDD) and a video tape recorder (VTR), a printing apparatus such as a laser beam printer (LBP), and an optical apparatus such as a compact disk (CD), a CD-ROM, a digital video disk (DVD), and a DVD-ROM.

[0042] Other features of this invention will become apparent in the course of the following description of exemplary embodiments, which are given for illustration of the invention and are not intended to be limiting thereof.

EXAMPLES 1 TO 6

[0043] In each Example, the base oil, the thickener, and the antioxidant shown in TABLE 1 were used. Diisocyanate dissolved by heating in the base oil to prepare a mixture. The amine shown in TABLE 1 dissolved by heating in the mixture to prepare another mixture. Both the mixtures were mixed to prepare a gel. The amount of the amine was two times that of the diisocyanate by a mole ratio. The antioxidant was added to the gel. The gel was stirred, and passed through a roll mil to prepare semi-solid state lubricant grease as a lubricant composition. In TABLE 1, the content of each material is described in % by weight based on 100% by weight of the total composition.

[0044] In TABLE 1, worked penetration of the resultant lubricant grease, and viscosity of the base oil used are shown. Also, acoustic properties and fretting corrosion measured as described below are shown in TABLE 1.

[0045] 1) Acoustic properties

[0046] The lubricant grease was applied to two 684 bearings, each of which was a deep groove ball bearing having an inside diameter of 4 mm, and an outer diameter of 9 mm. The 684 bearings were set to a rotation axis which rotates by one spindle motor. The bearings were rotated under the conditions that the bearing rotation speed was 2000 rpm, atmosphere temperature was 100° C., and an axial load was 0.8 kgf. A value of noise (dBA) was measured every 100 hours in accordance with JIS B1548-1960.

[0047] When the value of noise was less than 42 dBA, the bearings were rotated again under the same conditions, and the value of noise was measured again after 100 hours. The measurement was repeated until the value of noise reached to 42 dBA. A time to reach to 42 dBA was recorded to determine acoustic properties. The acoustic properties are evaluated as described below, and the evaluation results are shown in TABLE 1.

[0048] good: It took 600 hours or more until the value of noise reached to 42 dBA.

[0049] not good: It took not less than 300 hours to less than 600 hours until the value of noise reached to 42 dBA.

[0050] bad: It took less than 300 hours until the value of noise reached to 42 dBA.

[0051] 2) Fretting corrosion

[0052] The lubricant grease was applied to inside of 51204 bearing, which was a thrust ball bearing having an inside diameter of 20 mm, and an outer diameter of 40 mm. The bearing was vibrated continuously for 2 hours under the conditions that a frequency was 30 Hz, an oscillating angle was 12 degree, atmosphere was room temperature, and an axial load was 2450 N. After the test, the bearing was weighed to determine a weight decrease caused by wearing. Fretting corrosion is evaluated as described below, and the evaluation results are shown in TALBE 1. The lesser the weight decrease is, the higher the fretting corrosion resistant of the lubricant grease is.

[0053] good: The weight decrease caused by wearing was less than 2 mg.

[0054] not good: The weight decrease caused by wearing was not less than 2 mg to less than 3 mg.

[0055] bad: The weight decrease caused by wearing was 3 mg or more. TABLE 1 Example Composition 1 2 3 4 5 6 Base oil Ether oil*1 — — 9 22 — 8.4 Ester oil*2 — — — — — — Synthesized hydrocarbon oil*3 85.5 86.5 77.5 63.5 83.5 75.1 Thickener Amine Octylamine 3.8 6.6 6.6 6.1 9.6 9.6 Cyclohexylamine 2.9 — — — — — p-toluidine — — — — — — Diisocyanate MDI*4 7.3 6.4 6.4 5.9 — — TDI*5 — — — — 6.4 6.4 12-hydroxy Li stearate — — — — — — Antioxidant*6 0.5 0.5 0.5 0.5 0.5 0.5 Properties Viscosity (at 40° C., mm²/s) of base oil 46 46 36 44 46 36 Worked penetration (JIS K2220) 220 240 250 290 240 260 Acoustic properties good good good good good good Fretting corrosion resistance good good good good good good

Comparative Examples 1, 2 and 6

[0056] In each Comparative Example, the base oil, the thickener, and the antioxidant shown in TABLE 2 were used. Diisocyanate dissolved by heating in the base oil to prepare a mixture. The amine shown in TABLE 2 dissolved by heating in the mixture to prepare another mixture. Both the mixtures were mixed to prepare a gel. The amount of the amine was two times that of the diisocyanate by a mole ratio. The antioxidant was added to the gel. The gel was stirred, and passed through a roll mil to prepare semi-solid state lubricant grease as a lubricant composition. In TABLE 2, the content of each material is described in % by weight based on 100% by weight of the total composition.

[0057] In TABLE 2, worked penetration of the resultant lubricant grease, and viscosity of the base oil used are shown. Also, acoustic properties and fretting corrosion measured as the same procedures in Example 1 are shown in TABLE 2.

Comparative Examples 3 to 5

[0058] In each Comparative Example, the base oil, the thickener, and the antioxidant shown in TABLE 2 were used, and mixed by heating them at a melting point of the thickener or more, dissolved uniformly, and then cooled to prepare a gel. The gel was passed through a roll mil to prepare semi-solid state lubricant grease as a lubricant composition. In TABLE 2, the content of each material is described in % by weight based on 100% by weight of the total composition.

[0059] In TABLE 2, worked penetration of the resultant lubricant grease, and viscosity of the base oil used are shown. Also, acoustic properties and fretting corrosion measured as the same procedures in Example 1 are shown in TABLE 2. TABLE 2 Comparative Example Composition 1 2 3 4 5 6 Base oil Ether oil*1 — — — — — 86.5 Ester oil*2 86.5 — 87.5 43 — — Synthesized hydrocarbon oil*3 — 75.5 — 43 pta 85.5 — Thickener Amine Octylamine 6.6 — — — — 6.6 Cyclohexylamine — — — — — — p-toluidine — 11.1 — — — — Diisocyanate MDI*4 6.4 12.9 — — — 6.4 TDI*5 — — — — — — 12-hydroxy Li stearate — — 12 13.5 14 — Antioxidant*6 0.5 0.5 0.5 0.5 0.5 0.5 Properties Viscosity (at 40° C., mm²/s) of base oil 38 30 33 32 31 97 Worked penetration (JIS K2220) 240 290 210 220 240 280 Acoustic properties good bad good not bad not good good Fretting corrosion resistance bad good not good good bad bad

[0060] As shown in TABLE 1, in each Examples in which the urea compound was used as the thickener, not less than 50% by weight of the synthesized hydrocarbon oil, i.e., non-ester oil, was used as the base oil, there were provided excellent acoustic properties and fretting corrosion resistance.

[0061] As shown in TABLE 2, in Comparative Examples 1 and 3 in which the ester oil was used, there were provided poor fretting corrosion resistance. In Comparative Example 4 in which less than 50% by weight of the synthesized hydrocarbon oil was used, there was provided less fretting corrosion resistance as compared to those in Examples. In Comparative Example 6 in which the base oil containing no synthesized hydrocarbon oil was used, there was provided poor fretting corrosion resistance, and insufficient acoustic properties. In Comparative Example 2 in which the urea compound in which R² is an aromatic group, there provided high worked penetration, and poor acoustic properties.

[0062] In view of the above, it can be concluded that the lubricant composition of the present invention provides excellent acoustic properties and fretting corrosion resistance when it is applied to a bearing. In addition, the worked penetration of the lubricant composition according to the present invention is within the range of 220 to 280, thereby further enhancing the acoustic properties and the fretting corrosion resistance.

[0063] Furthermore, the bearing prelubricating the lubricant composition of the present invention is noise resistant, and fretting corrosion resistant. The bearing according to the present invention is suitable for a spindle bearing for use in an apparatus for recording and reading electronic information. 

What is claimed is:
 1. A lubricant composition, comprising: a base oil comprising a non-ester oil containing a synthesized hydrocarbon oil, and a thickener comprising a urea compound; wherein the urea compound is represented by the formula (I): R₁—(NHCONH—R₂)_(n)  (I) where R₁ is a group containing an aromatic hydrocarbon, R₂ is at least one hydrocarbon group selected from the group consisting of an alicyclic hydrocarbon group having 6 to 12 carbon atoms and an aliphatic hydrocarbon group having 6 to 20 carbon atoms, and n is 2 or 3; wherein the synthesized hydrocarbon oil has kinetic viscosity of 20 mm²/s or more and less than 80 mm²/s at 40° C.; and wherein the base oil comprises 50% by weight or more of the synthesized hydrocarbon oil based on the total weight of the base oil.
 2. The lubricant composition as claimed in claim 1, wherein the synthesized hydrocarbon oil is at least one selected from the group consisting of an aliphatic hydrocarbon oil and an aromatic hydrocarbon oil.
 3. The lubricant composition as claimed in claim 1, wherein the synthesized hydrocarbon oil is an aliphatic hydrocarbon oil.
 4. The lubricant composition as claimed in claim 3, wherein the aliphatic hydrocarbon oil is at least one selected from the group consisting of poly-α-olefine oil and a copolymer of α-olefine and olefine.
 5. The lubricant composition as claimed in claim 1, wherein the synthesized hydrocarbon oil is mixed with at least one hydrocarbon oil selected from the group consisting of a mineral oil such as naphthene, paraffin, liquid paraffin, and hydrodewaxed oil; a polyglycol oil such as polyalkylene glycol; an ether oil such as alkyldiphenyl ether, and polyphenyl ether; and a silicone oil such as polydimethyl siloxane, and polyphenyl methyl siloxane.
 6. The lubricant composition as claimed in claim 5, wherein the synthesized hydrocarbon oil is the ether oil.
 7. The lubricant composition as claimed in claim 1, wherein the R₁ has an aromatic single ring, an aromatic condensed ring, an aromatic single ring combined with methylene, cyanuric ring or isocyanuric ring, or an aromatic condensed ring combined with methylene, cyanuric ring or isocyanuric ring.
 8. The lubricant composition as claimed in claim 7, wherein the R₁ is a residual group in which an isocyanate group is eliminated from diphenylmethanediisocyanate, tolyleneduisocyanate, or a duisocyanate polymer.
 9. The lubricant composition as claimed in claim 8, wherein the R₁ is diphenylmethanediisocyanate or tolylenediisocyanate.
 10. The lubricant composition as claimed in claim 1, wherein the urea compound is a reaction product of at least one disocyanate selected from the group consisting of diphenylmethanediisocyanate and tolylenedusocyanate, and at least one amine compound selected from the group consisting of octylamine, cyclohexylamine, and toluidine.
 11. The lubricant composition as claimed in claim 1, having worked penetration of 220 to
 280. 12. A ball-and-roller bearing with a smaller diameter prelubricating a lubricant composition, wherein the lubricant composition comprises a base oil comprising a non-ester oil containing a synthesized hydrocarbon oil, and a thickener comprising a urea compound; wherein the urea compound is represented by the formula (I): R₁—(NHCONH—R₂)_(n)  (I) where R₁ is a group containing an aromatic hydrocarbon, R₂ is at least one hydrocarbon group selected from the group consisting of an alicyclic hydrocarbon group having 6 to 12 carbon atoms and an aliphatic hydrocarbon group having 6 to 20 carbon atoms, and n is 2 or 3; wherein the synthesized hydrocarbon oil has kinetic viscosity of 20 mm²/s or more and less than 80 mm²/s at 40° C.; and wherein the base oil comprises 50% by weight or more of the synthesized hydrocarbon oil based on the total weight of the base oil.
 13. The ball-and-roller bearing as claimed in claim 12, which is noise resistant and fretting corrosion resistant.
 14. The ball-and-roller bearing as claimed in claim 12, which is a spindle bearing for use in an apparatus for recording and reading information. 